i too think that is CPU related
I just went from an 8800GTS 320MB OC to a 9800GTX+ 512 Superclocked edition and saw a small minimal increase in FPS ... when I run the game it seems the GPU is not even being used to its potential while my CPU (E7200 C2D running 3.17GHZ) is running from 88% to 95% load at all times
System Specs
Windows 7 RC
E7200 C2D Running at 3.17 GHZ
4 gig of 6400 ram
9800 GTX+ 512 Superclocked
1440 x 900
settings all over the place from low to high ... fps range in open with nothing going on around 35 - 45 ... buildings / trees hits 15 - 25 ... i would say average is 25 - 30